A synthetic aperture radar (SAR: Synthetic Aperture Radar) is a device that is mounted in a moving object, such as a satellite or an airplane, and that observes an object, such as an earth surface, with a high resolution. This radar usually emits a radio wave toward a direction nearly perpendicular to the direction of movement of the moving object. The radar carries out the observation on a region on the ground to which the radio wave is applied by acquiring a resolution with respect to a direction parallel to the direction of movement of the moving object through a synthetic aperture process, and also acquiring a resolution with respect to a direction of emitting the radio wave (direction of the distance) through a pulse compression process.
In this case, the synthetic aperture process is the one of improving the angular resolution. In general, the angular resolution of the radar is determined by the size of the antenna which is used when emitting the radio wave to space, and the larger aperture the antenna has, the higher angular resolution is acquired. However, in a case in which a radar is mounted in a moving object, a limitation is imposed on the size of an antenna which can be mounted in the radar. To solve this problem, an SAR provides an angular resolution equivalent to that of an antenna having an aperture of the same size as the length of a moving path by carrying out observation while moving, and combining received signals which are acquired during a fixed time period by performing signal processing. For example, an example of the signal processing method is shown in patent reference 1. In this patent reference 1, in order to acquire a high resolution image, high-accuracy signal processing in consideration of the satellite's orbit being a curved line is carried out.